Optical module with can package

1. An optical module with a CAN package, comprising: a stem configured to have a hole penetrating said stem and an inner cylindrical surface surrounding said hole; and a lead configured to extend through said hole such that a gap exists between said lead and said inner cylindrical surface, wherein said gap contains a first portion and a second portion which are arranged along the longitudinal direction of said hole, and wherein said first portion is filled with sealing material which is dielectric and said second portion is filled with air.

2. The optical module according to claim 1 , wherein said lead, said gap and said stem are an inner conductor, dielectric and outer conductor of a coaxial line, respectively.

3. The optical module according to claim 1 , wherein said sealing material is glass.

4. The optical module according to claim 1 , wherein the length of said first portion along said longitudinal direction is 80% or more and less than 100% of the length of said hole along said longitudinal direction.

5. The optical module according to claim 1 , wherein said gap further contains a third portion which is filled with air, and wherein said second portion, said first portion and said third portion are arranged along said longitudinal direction in that order.

6. The optical module according to claim 1 , further comprising: chip parts, wherein said stem has a front surface and a back surface, wherein said hole penetrates said stem from said front surface to said back surface, and wherein said chip parts are mounted on said front surface.

7. The optical module according to claim 1 , further comprising a pre-amplifier; and a bonding wire, wherein said stem has a front surface and a back surface, wherein said hole penetrates said stem from said front surface to said back surface, wherein said pre-amplifier is mounted on said front surface, and wherein said bonding wire connects the lead and the pre-amplifier.

8. The optical module according to claim 1 , further comprising: a cap, wherein said stem has a front surface and a back surface, wherein said hole penetrates said stem from said front surface to said back surface, wherein said cap covers said front surface, and wherein said first portion is placed adjacent to said back surface and said second portion is placed adjacent to said front surface.

9. The optical module according to claim 1 , further comprising: a cap; a light receiving element, wherein said stem has a front surface and a back surface, wherein said hole penetrates said stem from said front surface to said back surface, wherein said cap covers said front surface, wherein said light receiving element is mounted on said front surface, wherein said lead has a first end which protrudes beyond said front surface and a second end which protrudes beyond said back surface, wherein said first end is electrically connected to said light receiving element, and wherein said light receiving element is configured to receive an optical signal through said cap, to convert said optical signal into an electric signal and to output said electric signal through said second end.

10. An optical module with a CAN package comprising: a first coaxial line which contains a first inner conductor, a first outer conductor and a first dielectric between said first inner conductor, and said first outer conductor; a second coaxial line which contains a second inner conductor, a second outer conductor and a second dielectric between said second inner conductor and said second outer conductor, wherein said first coaxial line and said second coaxial line are connected in series, and wherein said first dielectric is glass and said second dielectric is air.